How to make back button return to the system Windows Phone - windows-phone-7

Question

I have a small app there is 3 seconds intro page, then the content page. When I push back button I go back to the intro screen, but I think I should go back to the system. How to do it?
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Phone.Controls;
using System.ServiceModel.Syndication;
using System.Xml;
using Microsoft.Phone.Tasks;
namespace RSS {
public partial class FeedPage : PhoneApplicationPage {
public FeedPage() {
InitializeComponent();
this.Loaded += new RoutedEventHandler(PhonePage1_Loaded);
}
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e) {
clearBackStack();
base.OnNavigatedTo(e);
}
void clearBackStack() {
while (this.NavigationService.BackStack.Any()) {
this.NavigationService.RemoveBackEntry();
}
}
void PhonePage1_Loaded(object sender, RoutedEventArgs e) {
// clearBackStack();
WebClient wc = new WebClient();
wc.OpenReadCompleted += new OpenReadCompletedEventHandler(wc_OpenReadCompleted);
wc.OpenReadAsync(new Uri("http://www.carmagazine.co.uk/Shared/Handlers/RssHandler.ashx?&N=190&Ns=P_Publication_Date|1&?"));
}
void wc_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e) {
SyndicationFeed feed;
try {
using (XmlReader reader = XmlReader.Create(e.Result)) {
feed = SyndicationFeed.Load(reader);
lista.ItemsSource = feed.Items;
}
} catch (WebException we) { MessageBox.Show("Internet connection is down.");}
}
private void Button_Click(object sender, System.Windows.RoutedEventArgs e) {
WebBrowserTask webBrowserTask = new WebBrowserTask();
String url = (String)((Button)sender).Tag;
webBrowserTask.Uri = new Uri(url);
webBrowserTask.Show();
}
}
}

Answer 1

You should clear the BackStack in the OnNavigateTo method of your content page
while (this.NavigationService.BackStack.Any())
{
this.NavigationService.RemoveBackEntry();
}

Answer 2

The following code is the best practice for the back button key press.
protected override void OnBackKeyPress(CancelEventArgs e)
{
while (NavigationService.CanGoBack)
NavigationService.RemoveBackEntry();
base.OnBackKeyPress(e);
}
This ensures that your application will exit and return to the main screen on pressing the BackKey.